BACKGROUND: We evaluated use of the ARCHITECT HIV Ag/Ab Combo assay (HIV Combo; Abbott Diagnostics; available for sale outside the United States only) for detection of acute HIV infection. METHODS: Samples were obtained from a behavioral intervention study (EXPLORE). HIV-uninfected men who have sex with men were enrolled and tested for HIV infection every 6 months. Samples from seroconverters collected at their last seronegative visit (n = 217) were tested individually using 2 HIV RNA assays. Samples with detectable HIV RNA were classified as acute and were tested with HIV Combo. Samples from the enrollment visit (n = 83) and the time of HIV seroconversion (n = 219) were tested with HIV Combo as controls. RESULTS: Twenty-one samples (9.7%) from the last seronegative visit had detectable HIV RNA and were classified as acute. HIV Combo was positive for 13 of the acute samples (61.9%). Samples not detected by HIV Combo had viral loads of 724-15,130 copies per milliliter. Expected results were obtained for positive and negative controls tested with HIV Combo. CONCLUSIONS: HIV Combo detected nearly two thirds of acute HIV infections identified in this high-risk population by non-pooled HIV RNA assays. HIV Combo may be useful for high-throughput screening to identify individuals with acute HIV infection.